1. Field of the Invention
This invention relates generally to radiation sensors and more particularly to bolometer type sensors for detecting thermal radiation.
2. Description of Related Art
Bolometers are well known in the art and comprise thermal devices which generate an electrical output when they are heated by the energy that they absorb. These devices have many applications and they are currently finding new applications, particularly in the field of infra-red (IR) imaging. Imaging in the long wave infra-red (LWIR) band of the electromagnetic spectrum has been achieved and efforts are currently under way to extend its capability to the millimeter wave (MM) and Terahertz (THz) spectral bands of the electromagnetic spectrum.
The inherent limitations in conventional bolometers has now been overcome with the use of semiconductor IR detector devices such as silicon diodes. In a related invention of the present applicant, a semiconductor thermocouple arrangement comprising a pair of back-to-back bolometer devices comprising silicon diodes as shown and described in U.S. Pat. No. 6,489,615 entitled “Ultra-sensitive Silicon Sensor”, dated Dec. 3, 2002, the contents of which are intended to be incorporated herein by reference, are respectively located in a detector stage and an intermediate stage, the latter being located between the detector stage and a heat bath stage. This type of sensor achieves maximum thermal isolation between the silicon diode temperature detectors and the outside world. Thermal isolation is achieved by using electro-thermal feedback which is provided by the heat generated by an amplifier physically located in the intermediate stage and which generates heat which is proportioned to the difference between the temperatures detected by the silicon diodes respectively located in the detector stage and the intermediate stage. The heat generated by the amplifier zeroes the temperature difference between the detector stage and the intermediate stage, and thereby zeroes any net heat flowing between the detector stage and the intermediate stage, thus enhancing the sensitivity of the diode sensors to thermal radiation.